1. Field of the Invention
The present invention relates to a process for purification of the alkali metal salt of sulfonated unsaturated aliphatic carboxylic acid, and more particularly, to an efficient extraction process whereby unreacted fatty acid impurities are separated from the sulfonated carboxylic acid salt.
2. Description of the Prior Art
Sulfonated unsaturated aliphatic carboxylic acids are well known, and the commercial process for production thereof is given in U.S. Pat. No. 2,743,288, issued Apr. 24, 1956. Theses salts of sulfonated unsaturated carboxylic acids have found use in the detergent industry, and the sodium salt of sulfonated oleic acid is particularly valuable. However, the commercial products generally contain a certain amount of impurities such as unreacted saturated fatty acids. These acids cause insoluble precipitates in formulated acid-type sanitizers such as in the formulation described in U.S. Pat. No. 3,650,954 and the disclosure of this patent is incorporated by reference herein. The fatty acids are particularly troublesome when the sanitizer is utilized at low temperatures, because the impurities then precipitate out, and the precipitate even remains when the sanitizer solution is returned to room temperature.
At the time of the invention, the closest known prior art was U.S. Pat. No. 2,743,288 wherein the production of the sodium salt of sulfonated oleic acid and the like is disclosed. In the patent, purification by extraction is suggested, but it is stated that, for most purposes, extraction is unnecessary because of the small amount of unreacted materials in the product. A typical extraction process is disclosed in Example 1 wherein the product is extracted with three separate extractions of petroleum ether. As disclosed in the patent, considerable impurities are removed in the second and third extractions and the extracted material is primarily stearic acid. Accordingly, it is seen that the extractions suggested by the patentee are not commercially suitable for purification of the product.
Other techniques have been tried for the removal of unreacted fatty acid impurities such as, precipitation by cooling, followed by filtration. However, none of these other techniques have been commercially satisfactory.